A gas turbine engine may be used to supply power to various types of vehicles and systems. For example, gas turbine engines may be used to supply propulsion power to an aircraft. Many gas turbine engines include at least three major sections, a compressor section, a combustor section, and a turbine section. The compressor section receives a flow of intake air and raises the pressure of this air to a relatively high level. In a multi-spool (e.g., multi-shaft) engine, the compressor section may include two or more compressors. The compressed air from the compressor section then enters the combustor section, where a ring of fuel nozzles injects a steady stream of fuel. The injected fuel is ignited by a burner, which significantly increases the energy of the compressed air.
The high-energy compressed air from the combustor section then flows into and through the turbine section, causing rotationally mounted turbine blades to rotate and generate energy. The air exiting the turbine section is then exhausted from the engine. Similar to the compressor section, in a multi-spool engine the turbine section may include a plurality of turbines. The energy generated in each of the turbines may be used to power other portions of the engine.
In addition to providing propulsion power, a gas turbine engine may also, or instead, be used to supply either, or both, electrical and pneumatic power to the aircraft. For example, some gas turbine engines include a bleed air port between the compressor section and the turbine section. The bleed air port allows some of the compressed air from the compressor section to be diverted away from the turbine section via a bypass duct, and used for other functions such as, for example, the aircraft environmental control system, the cabin pressure control system, and/or the aircraft thermal anti-ice (TAI) system.
Recent aircraft bleed air system designs require cooling of the high pressure bleed air. Accordingly, flush inlet scoops are often used to minimize fan duct losses and to maintain high volumetric flow rates through the bleed air duct system, thereby cooling the high pressure bleed air. Depending on the cooling requirements, the airflow through the fan bleed air duct system varies. Problems may occur when the fan bleed flow requirements are zero, and the control system closes the valve for the fan bleed air duct system. When the valve is in a closed position, a resonance chamber is formed from which a Helmholtz resonance may be created, powered by airflow over the flush scoop. The occurrence of the resonance may increase the noise signature of the engine significantly, and may cause the vibration levels of the engine system to increase above the set limits of the installation. This in turn can adversely impact overall operational efficiency and costs.
Hence, there is a need for a system for reducing resonance occurrences in bleed air ducts that, as compared to present systems, exhibits reduced noise signatures in the engine during normal bleed air operations, does not adversely impact gas turbine engine efficiency, and/or does not adversely impact overall operational efficiency and cost. The present invention addresses one or more of these needs.